Gear Ratios ???

[FJB20]

I've seen outdrives with 1.62 1.50 1.36 --What Does All that Mean? Lower the Number More Performance or Out of the Hole. Somewhat like the difference between 3.55 and 4.11 in a Car.
Thanx!!

[mattyboy]

1 : 1.61 = 1 rev of the engine to 1 and 61/100 revs of the prop or at 1000rpm the props spins 1610 times. you will find the higher ratio's are for smaller engines like a 4 cyl will be 1:1.84, but the higher the ratio means more teeth more teeth mean thinner teeth thin teeth weaker gears so on bigger engines the ratio is lower my
volvo 250b with a 351w is 1:1.61

Matt

[mattyboy]

I stand corrected I have the ratio bassackwards it would be at 1610 engine rpms the prop turns 1000 times. sorry see what happens when your mouth is in gear and your brain isn't eek! :p
Matt

[boldts]

Gear ratios work together with the size prop that is run on the boat. A 1.84 behind a 4 cyl engine allows that engine to turn a larger prop diameter and prop pitch. Most of your V-8 engines will come with a 1.5 or smaller number ratio because of the increased hp over the 4 cyl engine. If you water ski, you want quick out of the hole performance. The easiest way to get that is to lower the props pitch, but now you may have to be weary of over revving your engine in none skiing uses.

Once large hp engines such as turbo charged or super charged engines are installed, because prop sizes to match the additional hp are not always available, usually a taller or smaller number gear is installed so that you now need a smaller pitch or diameter prop on the boat to fit what is being built by prop manufactures.

The biggest key in boat performance is the torque that your engine can produce at 5000 to 5500 RPMs. If your engine with a say 1.36 gear behind it can still turn a 30" pitch prop at 5000 RPM, the speed is greatly increased! :D eek! :D

No expert here, so I may not be correct with everything said, but I have a 1.36 in front of a 454MAG. While most owners are turning 23" to 25" pitch by 15+" diameter props with a 1.50 gear ratio, my Classic runs a 22" pitch by 14 1/4 diameter prop at 4600 RPMs. This prop was selected because it optimizes my current set-up. My boat used to have one of those 15+" by 23" props on it when I purchased it. I gained 3 MPH simply by putting a more compatible to the set-up prop on the boat. Next step? Add the big hp the boat used to have back in her and start all over again with prop testing and research. wink

[mattyboy]

ok ok how bout the wheels on the bus go round and round!!!! wink :D :p


Matt